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org 0x500
bits 16

_init:
	cli				; clear interrupts
	xor	ax, ax			; null segments
	mov	ds, ax
	mov	es, ax
	mov	ax, 0x9000			; stack begins at 0x0000-0xffff
	mov	ss, ax
	mov	sp, 0xFFFF
	sti
	call InstallGDT
	call _EnableA20
	
	cli				; clear interrupts

	mov	eax, cr0		; set bit 0 in cr0--enter pmode
	or	eax, 1
	mov	cr0, eax

	jmp	0x8:PMODE	; far jump to fix CS. Remember that the code selector is 0x8!
	

_EnableA20:

        cli

        call    a20wait
        mov     al,0xAD
        out     0x64,al

        call    a20wait
        mov     al,0xD0
        out     0x64,al

        call    a20wait2
        in      al,0x60
        push    eax

        call    a20wait
        mov     al,0xD1
        out     0x64,al

        call    a20wait
        pop     eax
        or      al,2
        out     0x60,al

        call    a20wait
        mov     al,0xAE
        out     0x64,al

        call    a20wait
        sti
        ret

a20wait:
        in      al,0x64
        test    al,2
        jnz     a20wait
        ret


a20wait2:
        in      al,0x64
        test    al,1
        jz      a20wait2
        ret

InstallGDT:

	cli                  ; clear interrupts
	pusha                ; save registers
	lgdt 	[toc]        ; load GDT into GDTR
	sti	                 ; enable interrupts
	popa                 ; restore registers
	ret	                 ; All done!

;*******************************************
; Global Descriptor Table (GDT)
;*******************************************

gdt_data: 
	dd 0                ; null descriptor
	dd 0 

; gdt code:	            ; code descriptor
	dw 0FFFFh           ; limit low
	dw 0                ; base low
	db 0                ; base middle
	db 10011010b        ; access
	db 11001111b        ; granularity
	db 0                ; base high

; gdt data:	            ; data descriptor
	dw 0FFFFh           ; limit low (Same as code)10:56 AM 7/8/2007
	dw 0                ; base low
	db 0                ; base middle
	db 10010010b        ; access
	db 11001111b        ; granularity
	db 0                ; base high
	
end_of_gdt:
toc: 
	dw end_of_gdt - gdt_data - 1 	; limit (Size of GDT)
	dd gdt_data 			; base of GDT

		
bits 32

PMODE:

mov	ax, 0x10	; set data segments to data selector (0x10)
mov	ds, ax
mov	ss, ax
mov	es, ax
mov	esp, 90000h		; stack begins from 90000h

_main:
jmp $

Code: Select all

00015055744i[CPU0  ] 0x0000000000008121>> jmpf 0x0008:058e : EA8E050800
00015055744e[CPU0  ] exception(): 3rd (13) exception with no resolution, shutdown status is 00h, resetting